Host & Guest extreme slow when using usb

Description

Whenever i synchronize my iPhone and there is something to sync (like voice memo's) then both the guest and the host become slow. Shutting down the guest or saving the state of the guest is not the solution, because the host will remain slow even if no applications are running on it. The entire system must be rebooted to get things working smoothly again. Note that when the system is slow the state of the guest may saved and re-spawned after the host reboot. The system will work fine for a short period until slowing down again so i suspect that the problem lies within VirtualBox's USB add on.

During the slowness, opening the task list in either or both the guest and the host shows that a lot of time is spent in idle time and that trivial tasks may consume 100% of CPU for short periods of time.

I use Ubuntu 9.10 as host and have XP(sp3) as guest. The guest has only the following installed on it: MS Security Essentials, iTunes and Office since i use it exclusively for synching my iPhone and write documents for work that require office file formats.